Why Do `const` Namespace-Scope Variables in C Have Internal Linkage?

Understanding Internal Linkage Implications of const in C

In C , const member variables declared at namespace scope exhibit internal linkage behavior, unlike in C where they would have external linkage. To clarify, internal linkage implies that the identifier can be used only within the translation unit where it is declared, while external linkage allows identifiers to be referenced across multiple translation units.

This distinction arose specifically due to the unique nature of const objects in C . As explained in Appendix C of the C 11 standard (C.1.2), the ability for const objects to serve as compile-time constants prompted a departure from C-style behavior. By defaulting to internal linkage for const namespace-scope objects, C encourages programmers to provide explicit initializer values and allows for convenient inclusion of const objects in header files that are referenced in multiple compilation units.

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